
#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <errno.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <signal.h>
int g_child_stop = 0;
int g_parent_run = 0;
void sig_child(int signum)
{
 if( SIGUSR1 == signum )
 {
 g_child_stop = 1;
 }
}
void sig_parent(int signum)
{
 if( SIGUSR2 == signum )
 {
 g_parent_run = 1;
 }
}
int main(int argc, char **argv)
{
 int pid;
 int wstatus;
 signal(SIGUSR1, sig_child);
 signal(SIGUSR2, sig_parent);
 if( (pid=fork()) < 0 )
 {
 printf("Create child process failure: %s\n", strerror(errno));
 return -2;
 }
 else if(pid == 0)
 {
 /* child process can do something first here, then tell parent process to start running */
 printf("Child process start running and send parent a signal\n");
 kill(getppid(), SIGUSR2);
 while( !g_child_stop )
 {
 sleep(1);
 }
 
 printf("Child process receive signal from parent and exit now\n");
 return 0;
 }
 printf("Parent hangs up untill receive signal from child!\n");
 while( !g_parent_run )
 {
 sleep(1);
 }
 /* parent process can do something here, then tell child process to exit */
 printf("Parent start running now and send child a signal to exit\n");
 kill(pid, SIGUSR1);
 /* parent wait child process exit */
 wait(&wstatus);
 printf("Parent wait child process die and exit now\n");
 return 0;
}
